-[As I said, there was an extremely strange bug...]-
While this seems strange, it is quite common in this type of simulation,
even without passing the parameters wrongly. Reducing the time-step of the
simulation can delay the onset of this, as can changing the method of
numerical integration used (the position=position+velocity method is called
Euler Integration, and is the simplest method, but one of the least
accurate). The most commonly used method here is called 4th-order
Runge-Kutta - for this simulation, though, it seems not to be necessary to
complicate matters with this.

The reason why I _really_ like this simulation isn't because of the pov-ray
elements - its because of its musical potential. The simulation of the
resonances in gongs and drums can be simulated by linked masses like this.
Usually the links between masses are linear springs - however, from your
description (and from the appearence of the video) it looks like you're
using non-linear springs, which cause lots of internal resonances in the
grid. These could make interesting sounds if the position of the masses is
summed and outputted (speeded up many times) as a waveform.

http://homepage.ntlworld.com/thegablehouse/chris-j/phmms.html is a program
I've written to do this with linear springs - I never had much success with
non-linear springs, but your animation shows that it seems to be possible to
get interesting behaviour.

-Chris

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